1. Field of the Invention
This invention relates to system boot and more particularly to memory initialization during system boot.
2. Description of the Related Art
Computing systems are information handling systems which are designed to give independent computing power to one or more users. Computing systems can be found in many forms including, for example, mainframes, minicomputers, workstations, servers, personal computers, internet terminals, notebooks and embedded systems. Personal computer (PC) systems include desk top, floor standing, or portable versions. A typical PC system is a microcomputer that includes a microprocessor, associated memory and control logic (typically on a system board) and a number of peripheral devices that provide input and/or output (I/O) for the system. PC system boards often receive expansion PC boards to increase the capabilities of the computer system and to connect to peripheral devices through an expansion bus. For example, various multimedia devices are commonly implemented as add-in cards in desktop and portable computers or as integrated circuits for installation on a system board.
Computing systems typically include a set of built-in software routines called the basic input/output system (BIOS). The BIOS is a software interface between the system hardware and the operating system software. The BIOS facilitates programmer and user interaction with the system hardware. Because the BIOS has qualities of software and hardware, it is often referred to as firmware. The BIOS is a set of instructions to the computer's microprocessor. The BIOS is commonly coded using, for example, assembly language, and stored onto a non-volatile memory such as a ROM (Read Only Memory) or a PROM (Programmable ROM) such as an EPROM (Erasable PROM), an EEPROM (Electrically Erasable PROM), a flash RAM (Random Access Memory) or any other type of memory appropriate for storing BIOS.
The BIOS controls several important functions of personal computer systems. For instance, the BIOS performs various functions at power up, including testing and initializing memory, inventorying and initializing the system, and testing the system. These functions at power up are referred to as “system boot” or “booting the system” and can occur every time the system powers up or is reset. The BIOS also controls keystroke interpretation, display of characters, and communication via the PC ports.
FIGS. 1A–1B illustrate exemplary prior art computing system architectures. FIG. 1A illustrates an exemplary prior art single processor computing system architecture 100. BIOS executes on processor 102, referred to as the boot strap processor, to boot the computing system. Processor 102 can be any type of processor with any architecture, for example, a single scalar, a superscalar or a VLIW processor. As illustrated, processor 102 communicates through north bridge 104 to memory array 106. North bridge 104 includes a memory controller and one or more bridges to other devices. North bridge 104 communicates with one or more south bridges 108 on a standard bus 109, for example, a peripheral component interconnect (PCI) bus. South bridge 108 communicates to one or more input/output (I/O) devices 110 on another standard bus 111, for example, an ISA bus. Additional devices (not shown) can be attached to standard buses 109 and 111.
FIG. 1B illustrates an exemplary prior art multiprocessor computing system architecture 150. Architecture 150 is similar to architecture 100, except that multiple processors 152 communicate through a north bridge 154. Multiple processors 152 can share a common bus (not shown) to north bridge 154 or have individual communication paths as shown. Multiple processors 152 access memory array 106 through a memory controller in north bridge 154. One of the processors 152 is designated as the boot strap processor (BSP) and executes the BIOS to boot the computing system. During the boot process, the other processors 152 are inactive, for example, under a halt condition.
Memory array 106 can consist of several memory slots, populated or unpopulated, for the addition or replacement of memory modules. North bridges 104 and 154 can be programmed to interface to a variety of memory modules. As illustrated, the interface to memory array 106 is shared amongst the memory modules. Thus, if differing memory modules are populated, north bridges 104 and 154 must be programmed to parameters that allow each memory module to operate correctly. An exemplary memory module is illustrated in FIG. 4.
Upon system initialization, the BIOS executing on the boot strap processor initializes memory. Memory initialization can include verifying population of memory modules, verifying proper operation of the memory (no stuck bits), and initializing or clearing the memory to known values. Computer systems can have a large amount of memory, for example 8, 16 and even 32 Gigabytes of memory. Such systems can take several minutes to initialize the memory.
Architecture 150 is commonly used for servers which need extra processing power and have large amounts of memory. The boot strap processor performs all memory testing and clearing during system boot which can take a significant amount of time. Large server systems often take several minutes to boot while the other processors are idle.
To improve BIOS memory initialization time and thus the overall system boot time, some computing systems skip the initialization of the memory to known values. However, modern memory modules include error correction codes (ECC). These codes are used to find and correct memory bit errors. If the memory and ECC are not initialized to known values, extraneous errors remain upon system boot, resulting in an attempt to fix bogus errors and destroying good data. Additionally, large amounts of errors are logged. Thus, the initialization to known values cannot be skipped without causing system reliability problems.
ECC causes additional processing during system operation as well. ECC memory is “scrubbed” periodically during run-time when the computing system is not busy. By stepping through each memory address, errors can be found and corrected, eliminating the opportunities for multiple bit errors to accumulate that can't be corrected. Scrubbing memory improves memory reliability.